Bacteria growth can lead to disease, particularly when the species of bacteria is pathogenic. Even when a bacterial species is not normally pathogenic, a person or animal which is immunologically compromised may become infected with that bacterial species. While antibiotics are often used to combat such bacterial infections, bacteria can become resistent to those antibiotics and excessive use of antibiotics is frequently blamed for the occurrence of antibiotic-resistent bacteria. Moreover, many people are allergic to certain types of antibiotics and antibiotic usage can cause gastrointestinal upset or other side effects. For example, more than 75% of infants prescribed Amoxycillin.TM. or Augmentin.TM. develop diarrhea, which causes a four-fold increase in the probability of developing a diaper-area dermatology disease. Similarly, agricultural animals are healthier and more productive when bacterial exposure is reduced but antibiotic usage, with its attendant side effects and tendencies to give rise to antibiotic-resistent strains of bacteria, has been the only effective procedure for accomplishing these results. Hence, new methods are needed for preventing exposure of mammals to bacteria and for inhibiting bacterial growth once such exposure has occurred.
For example, methods for reducing bacterial growth in and on materials which are used near or by hospital patients, infants, the elderly and other persons whose immune systems are weakened, would greatly reduce the need for antibiotic usage. Similarly, methods for inhibiting bacterial growth in materials which contact the skin of such persons can prevent dermatological problems. Methods for inhibiting bacterial growth on surfaces used for food preparation would reduce the incidence of food poisoning. Methods of reducing bacterial growth in the litter, bedding and even the soil where domesticated animals are maintained would reduce animal mortality and increase yields of eggs, meat and milk.
Some materials are known to support bacterial growth, for example, the urine and feces captured by a diaper, but no method currently exists for inhibiting such growth. Even though it is initially sterile, bacteria and other microbes frequently begin to grow in urine and, when the skin is exposed to urine for any length of time, dermatological problems can result. Similarly, fecal material is rife with microorganisms that can cause dermatological problems, e.g. by producing proteolytic enzymes and lipases. These dermatological problems can also be created or exacerbated by ammonia formed by the breakdown of urea. The skin and tissues are irritated by ammonia at concentrations of 10,000 ppm; higher exposures produce burns and blistering. Adult tissues and moist membranes are irritated by ammonia gas at concentrations as low as 35 ppm for 15 minutes. See Proctor et al., Chemical Hazards of the Workplace (2d ed. 1988); 2B Patty's Industrial Hygiene and Toxicology 3045 (1981); Clayton and Clayton, Safety Standards for Industrial Chemicals (1981); NIOSH, Criteria for Recommended Standard Exposure to Ammonia (1981); American Conference of Governmental Industrial Hygienists (1987). Moreover, ammonia gas can be life-threatening to healthy adults at levels of about 1500 parts per million (ppm) over about two hours. The safe industrial limit of exposure to ammonia by adults is 35 to 50 ppm for 15 minutes. Breathing 5000 ppm can be immediately fatal. Bacterial growth exponentially increases the rate of ammonia formation.
Infants and the elderly can be even more sensitive to dermatological problems and to the effects of ammonia. For example, low birth weight infants often have underdeveloped respiratory systems which may be especially vulnerable to the toxic effects of ammonia. Infants and the elderly with any form of pulmonary disfunction such as bronchopulmonary dysplasia, chronic respiratory failure and pulmonary hypertension may succumb to ammonia poisoning more easily than healthy individuals.
For example, a baby urinates about 0.75 ml to 1.0 ml of urine per hour per kilogram of bodyweight. Urine is about 96% water, 2% urea and 2% other materials. The excreted urine passes through a membrane-sleeve of conventional disposable diapers, which are highly effective at absorbing water but not very effective at absorbing ammonia or ammonium ions. Moreover, while water is held tightly, a conventional diaper does not prevent microbial growth. In the presence of such microbes, urea present from excreted urine and feces begins to break down in minutes into ammonia and ammonium, by the following formulae: EQU CO(NH.sub.2).sub.2 +H.sub.2 O.fwdarw.CO.sub.2 +2NH.sub.3 EQU CO(NH.sub.2).sub.2 +2H.sub.2 O.fwdarw.HCO.sub.3.sup.- +NH.sub.4.sup.+ +NH.sub.3
The rate of in vitro ammoniation increases hourly by 5.8%, 6.3%, 8.0% and 9.7% through hours 2 to 5 after voiding. This steeply increasing rate of ammoniation is caused by growing colonies of bacteria and the consequent accumulation of urease which deaminates urea.
The pH of urine at the time of voiding is about 6.0, but, as NH.sub.4 OH and NH.sub.3 continually form over time the pH rises. At about three hours the pH is about 9.0 and NH.sub.3 gas flows continuously. While some microbial growth is retarded by pH 6.0 urine, an increased pH stimulates bacterial growth. Each urination provides fresh urea to start a new cycle of deamination. Ammonia is also formed by breakdown of microbial amino acids. This rising pH provides an increasingly hospitable environment for bacterial and other microbial colonies.
Moreover, even though the growth of microbes is momentarily slowed by a fresh voiding of pH 6.0 urine, such microbes quickly recover, continue growing and decompose more urea and amino acids.
Once ammonia gas is formed, it begins escaping back across a disposable diaper's membrane-sleeve where it contacts the skin and feces, if present. Ammonia elevates the pH of whatever medium it contacts. For example, the alkaline ammonia gas elevates the fecal pH which activates proteolytic enzymes that vigorously metabolize skin, causing irritations, rashes or lesions. Such damage makes the skin more vulnerable, not only to ammonia, but to opportunistic microbes, including fungi such as Candida, and bacteria that normally do not inhabit the skin.
When disposable diapers become saturated with urine, pressure of 0.5 psi will force urine back through the membrane-sleeve where it contacts skin and feces, a phenomenon known as "re-wetting." Frequently, disposable diapers become saturated and the membrane-sleeve bursts open, permitting urine to contact skin and feces. In either case, this urine is aged or ripe and contains deaminating urea, ammonium, ammonium hydroxide, dissolved ammonia, ammonia gas and carbon dioxide, as well as a potentially enormous inoculum of urea-cleaving bacteria. Large numbers of bacteria can be toxic, especially if they enter body cavities or if subdermal areas of the epidermis have been breached. The carbon dioxide is known to be toxic when breathed, and is believed to cause fatal hypercarbia to infants in certain conditions. See Thach, J. PEDIATRICS (June, 1993); Kemp & Thach, PEDIATRIC RES. (July 1994); Kinney et al. SCIENCE (September 1995). A combination of ammonia gas and carbon dioxide is believed to be more toxic than either gas alone.
According to the present invention, zeolites prevent microbial growth thereby inhibiting urea from converting to ammonia and carbon dioxide. Therefore, zeolites have two beneficial effects: inhibition of bacterial growth and inhibition of ammonia and carbon dioxide production.
Zeolites can be chemically synthesized and also occur naturally in volcanic rocks, altered basalts, ores and clay deposits. Zeolites include crystalline, hydrated alkali-aluminum silicates of the general formula: EQU M.sub.2/n O.(Al.sub.2 O.sub.3).y(SiO.sub.2)!.wH.sub.2 O
wherein M is a cation of valence n, w is the number of water molecules, and y is 2 or more. The cation is mobile and can undergo ion exchange. See U.S. Pat. No. 2,882,243 to Milton.
Zeolites have been used as catalysts, adsorbents and ion exchange media in chemical and hydrocarbon processing procedures. Some forms of crystalline aluminosilicate zeolites are regenerated after use in such procedures, often by acid treatment or thermal treatment at very high temperatures. Resistance to such treatment is related to the presence of a higher proportion of SiO.sub.2 relative to Al.sub.2 O.sub.3 in the aluminosilicate. See U.S. Pat. No. 3,691,099 to Young.
Crystalline, hydrated aluminous tectosilicates of Group I and II elements such as potassium, magnesium and calcium are also formed in nature or may be synthesized in the laboratory. Higher polyvalent ions, such as the rare earths, are readily introduced by cation exchange. Structurally, these tectosilicates form an aluminous silicate "framework" extending as an infinite three-dimensional network of AlO.sub.4 and SiO.sub.4 tetrahedra linked together by shared oxygen atoms. These aluminous tectosilicates are represented by the empirical unit cell formula: EQU M.sub.x/n (AlO.sub.2).sub.x (SiO.sub.2).sub.y !wH.sub.2 O
wherein M is a cation of valence n, w is the number of water molecules, x is the number of AlO.sub.2 units and y is the number of SiO.sub.2 units. The ratio of y/x is usually about 1 to about 10. The sum of x and y is the total number of tetrahedra in the unit cell.
Channels and pores uniformly penetrate the entire volume of the solid zeolite. When water is removed from these zeolites, large internal surface areas become available to absorb liquids or gases. Thus, the external surface area of a zeolite represents only a small portion of its total available surface area. Moreover, the dehydrated zeolite selectively absorb or reject different molecules on the basis of their effective molecular sizes and shapes.
Point electric charges on the surfaces of aluminous zeolite pores absorb highly polar molecules such as water, alcohols and the like. Such hydrophilicity has been exploited to remove water from polar substances which are less readily absorbed by the aluminous zeolite, for example, hydrocarbons processed by the petroleum industry. Gas streams may also be dried with a dehydrated zeolite due to its extremely strong attraction for water. Both naturally-occurring and synthetically-prepared zeolites have been used to remove nitrogenous components from liquid human and animal wastes by ion exchange. See U.S. Pat. No. 3,935,363 to Burholder. Metal catalysts have been introduced into zeolites for converting carbon monoxide to carbon dioxide or for catalyzing the hydrogenation and cracking of petroleum feedstocks. See British Patent No. 2,013,476A. Hydrophobic tectosilicates, developed to resist water absorption, will absorb less polar substances from mixtures containing water. See U.S. Pat. Nos. 4,744,374 and 4,683,318. For example, U.S. Pat. No. 3,682,996 to Kerr disclosed silylation of free hydroxy sites in zeolites by trimethylsilane (H--Si(CH.sub.3).sub.3) and that such silylated zeolites absorbed about 40% less cyclohexane, n-hexane and water than the parent "hydrogen" zeolites of type II. However, Kerr did not report any change in selectivity preference. Similarly, R. M. Barrer and J. -C. Trombe, J. C. S. Faraday I, 74, 1871 (1978), reported some nest silylation to form a tectosilicate of structure V (R=SiH.sub.3, x&lt;4) but were largely unsuccessful in replacing lattice aluminum with silicon, reporting that nest hydroxyl groups appeared to be less reactive to silylation than are the hydroxyl groups of the present structure II.
However, there has been no recognition of the present beneficial properties of either hydrophilic or hydrophobic zeolites for preventing microbial growth and for preventing the conversion of urea and amino acids to ammonia. Instead, skin rashes and irritations are frequently treated with salves and ointments. For example, U.S. Pat. No. 4,556,560 to Buckingham provides a lipase-inhibiting agent which is preferably applied with a barrier-like vehicle for treatment of diaper rash and diaper dermatitis. Medicated greases such as Balmex.RTM. and A&D Ointment.RTM. are also widely available. However, while these products may provide some protection from ammonia burns, they also block oxidation of the injured skin and create an ideal environment for growth of anaerobic bacteria. Therefore, a long-standing need exists for a new solution to dermatological problems such as diaper rash and dermatitis.